Implants formed of coupled bone

ABSTRACT

The present invention relates to an implant comprising two or more bone fragments that are combined to form a single unit. Cancellous bone or cortical bone is removed from a source and fashioned into bone components with desirable shapes and sizes. The bone components may be integrated to form implants for implantation in the body. Bone stock may be formed by combining sections of various bones of the body, and the bone stock may be further fashioned for use as implants with particular geometries.

CROSS-REFERENCE TO RELATED APPLICATIONS

The benefit of provisional application No. 60/191,099, filed Mar. 22,2000, is claimed under 35 U.S.C. § 119(e). This application also is acontinuation of prior patent application Ser. No. 09/814,216, filed Mar.22, 2001, now U.S. Pat. No. 6,632,247.

FIELD OF THE INVENTION

The invention relates to an implant for orthopedic applications. Moreparticularly, the invention is related to an implant formed from two ormore bone portions.

BACKGROUND OF THE INVENTION

Bone grafts have become an important and accepted means for treatingbone fractures and defects. In the United States alone, approximatelyhalf a million bone grafting procedures are performed annually, directedo a diverse array of medical interventions for complications such asfractures involving bone loss, injuries or other conditionsnecessitating immobilization by fusion (such as for the spine orjoints), and other bone defects that may be present due to trauma,infection, or disease. Bone grafting involves the surgicaltransplantation of pieces of bone within the body, and generally iseffectuated through the use of graft material acquired from a humansource. This is primarily due to the limited applicability ofxenografts, transplants from another species.

Orthopedic autografts or autogenous grafts involve source bone acquiredfrom the same individual that will receive the transplantation. Thus,this type of transplant moves bony material from one location in a bodyto another location in the same body, and has the advantage of producingminimal immunological complications. It is not always possible or evendesirable to use an autograft. The acquisition of bone material from thebody of a patient typically requires a separate operation from theimplantation procedure. Furthermore, the removal of material, oftentimesinvolving the use of healthy material from the pelvic area or ribs, hasthe tendency to result in additional patient discomfort duringrehabilitation, particularly at the location of the material removal.Grafts formed from synthetic material have also been developed, but thedifficulty in mimicking the properties of bone limits the efficacy ofthese implants.

As a result of the challenges posed by autografts and synthetic grafts,many orthopedic procedures alternatively involve the use of allografts,which are bone grafts from other human sources (normally cadavers). Thebone grafts, for example, are placed in a host bone and serve as thesubstructure for supporting new bone tissue growth from the host bone.The grafts are sculpted to assume a shape that is appropriate forinsertion at the fracture or defect area, and often require fixation tothat area as by screws or pins. Due to the availability of allograftsource material, and the widespread acceptance of this material in themedical community, the use of allograft tissues is certain to expand inthe field of musculoskeletal surgery.

FIGS. 1A, 1B, 1C, and 1D show the relative sizes of the femur 10(thigh), tibia 11 (lower leg), humerus 12 (upper arm), and radius 13(lower arm) respectively for an adult. As can be seen when comparingthese bones, their geometry varies considerably. The lengths of thesebones may have a range, for example, from 47 centimeters (femur), to 26centimeters (radius). In addition, as shown in FIGS. 1E and 1F, theshape of the cross section of each type of bone varies considerably, asdoes the shape of any given bone over its length. While the femur 10, asshown in FIG. 1E, has a generally rounded outer shape, the tibia 11 hasa generally triangular outer shape as shown in FIG. 1F. The wallthickness also varies in different areas of the cross-section of eachbone. For example, femur 10 has a wall thickness X₁ that is much smallerthan wall thickness X₂. Similarly, tibia 11 has a wall thickness X₃ thatis much smaller than wall thickness X₄. Even after clearing the innercanal regions 14 and 15 within the bones, the contours of these canalsvary considerably. Thus, machining of the bone to have standardizedouter dimensions and/or canal dimensions is necessary in manyapplications.

Sections of bones with regions having narrow cross-sections, as seen forexample with thicknesses X₁ and X₃, may be rejected for use in certainapplications because the wall thickness does not have sufficientstrength. Preferably, no region of a bone section has a thickness lessthan 5 millimeters, although in some applications smaller wallthicknesses may be employed. Thus, in the case that a bone section isfound to have a region with a wall thickness less than a minimumacceptable thickness, such a bone section is rejected as beingunsuitable for use in a bulk configuration. Often, such a section isground into bone particulate that is then used in other applications.The minimum thickness standards imposed on the use of bone sectionsresults in the rejection of substantial quantities of bone sections, andthus an inefficient use of the material. Bone sections that do not meetthe minimum thickness standards are often found in older individuals.

As a collagen-rich and mineralized tissue, bone is composed of aboutforty percent organic material (mainly collagen), with the remainderbeing inorganic material (mainly a near-hydroxyapatite compositionresembling 3Ca₃(PO₄)₂·Ca(OH)₂). Structurally, the collagen assumes afibril formation, with hydroxyapatite crystals disposed along the lengthof the fibril, and the individual fibrils are disposed parallel to eachother forming fibers. Depending on the type of bone, the fibrils areeither interwoven, or arranged in lamellae that are disposedperpendicular to each other.

There is little doubt that bone tissues have a complex design, and thereare substantial variations in the properties of bone tissues withrespect to the type of bone (i.e., leg, arm, vertebra) as well as theoverall structure of each type. For example, when tested in thelongitudinal direction, leg and arm bones have a modulus of elasticityof about 17 to 19 GPa, while vertebra tissue has a modulus of elasticityof less than 1 GPa. The tensile strength of leg and arm bones variesbetween about 120 MPa and about 150 MPa, while vertebra have a tensilestrength of less than 4 MPa. Notably, the compressive strength of bonevaries, with the femur and humerus each having a maximum compressivestrength of about 167 MPa and 132 MPa respectively. Again, the vertebrahave a far lower compressive strength of no more than about 10 MPa.

With respect to the overall structure of a given bone, the mechanicalproperties vary throughout the bone. For example, a long bone (leg bone)such as the femur has both compact bone and spongy bone. Cortical bone,the compact and dense bone that surrounds the marrow cavity, isgenerally solid and thus carries the majority of the load in majorbones. Cancellous bone, the spongy inner bone, is generally porous andductile, and when compared to cortical bone is only about one-third toone-quarter as dense, one-tenth to one-twentieth as stiff, but fivetimes as ductile. While cancellous bone has a tensile strength of about10–20 MPa and a density of about 0.7, cortical bone has a tensilestrength of about 100–200 MPa and a density of about 2. Additionally,the strain to failure of cancellous bone is about 5–7%, while corticalbone can only withstand 1–3% strain before failure. It should also benoted that these mechanical characteristics may degrade as a result ofnumerous factors such as any chemical treatment applied to the bonematerial, and the manner of storage after removal but prior toimplantation (i.e. drying of the bone).

Notably, implants of cancellous bone incorporate more readily with thesurrounding host bone, due to the superior osteoconductive nature ofcancellous bone as compared to cortical bone. Furthermore, cancellousbone from different regions of the body is known to have a range ofporosities. Thus, the design of an implant using cancellous bone may betailored to specifically incorporate material of a desired porosity.

It is essential to recognize the distinctions in the types andproperties of bones when considering the design of implants. Surgeonsoften work with bones using similar tools as would be found incarpentry, adapted for use in the operating room environment. Thissuggests that bones have some properties which are similar to some typesof wood, for example ease in sawing and drilling. Notably, however, aremany differences from wood such as the abrasive nature of hydroxyapatiteand the poor response to local heating during machining of a bone. Thecombination of tensile and compressive strengths found in bone,resulting from the properties of the collagen and hydroxyapatite, isthus more aptly compared to the tensile and compressive strengths foundin reinforced concrete, due to steel and cement. Furthermore, while woodis readily available in considerable quantity, bone material is anextremely limited resource that must be used in an extremely efficientmanner.

Various types of bone grafts are known. For example, as disclosed inU.S. Pat. No. 5,989,289 to Coates et al., a spinal spacer includes abody formed of a bone composition such as cortical bone. The spacer haswalls that define a chamber that is sized to receive an osteogeniccomposition to facilitate bone growth.

U.S. Pat. No. 5,899,939 to Boyce et al. discloses a bone-derived implantfor load-supporting applications. The implant has one or more layers offully mineralized or partially demineralized cortical bone and,optionally, one or more layers of some other material. The layersconstituting the implant are assembled into a unitary structure, as byjoining layers to each other in edge-to-edge fashion in a manneranalogous to planking.

Another bone-grafting material is disclosed in U.S. Pat. No. 4,678,470to Nashef et al., and is formed using a tanning procedure involvingglutaraldehyde that renders the material osteoinvasive. A bone block isshaped into a precise predetermined form and size using conventionalmachining techniques. A paste-like suspension is also formed using knownmethods of comminuting bone, such as milling, grinding, and pulverizing,and adding the pulverized or powdered bone to a carrier. The treatmentwith glutaraldehyde allows the use of bovine, ovine, equine, and porcinebone sources. However, if the final desired form of the bone graftingmaterial is a block of bone or machined shape, the bone stock must belarge enough to provide a block of the required size.

U.S. Pat. No. 5,981,828 to Nelson et al. discloses a “composite”acetabular allograft cup for use in hip replacement surgery. A press isused to form the cup from impacted cancellous bone chips and cement. Thecomposite is a hollow hemispherical dome having an outer surfacecomprised essentially of exposed cancellous bone chips and an innersurface comprised essentially of hardened bone cement. The cancellousbone chips are first placed in a mold and subjected to a load to form acompact and consolidated mass that conforms to the shape of the mold.The mold is then opened, cement is applied, and the mold is thenreapplied. While an allograft of a particular shape may be formed usingthis process, the process is limited to forming an allograft bycompressing cancellous bone chips. Thus, numerous molds are required inorder to produce allografts of different sizes, and the use of bulk-sizeallograft source material is not facilitated.

With a rapidly increasing demand in the medical profession for devicesincorporating bone material, the tremendous need for the tissue materialitself, particularly allograft tissue material, presents a considerablechallenge to the industry that supplies the material. Due to the sizeand shape of the bones from which the material is harvested, and thedimensional limitations of any particular type of bone in terms ofnaturally occurring length and thickness (i.e. cortical or cancellous),there is a need for a means by which individual bone fragments can becombined to form larger, integral implants that are more suitable foruse in areas of larger fractures or defects. For example, the size ofcortical bone fragments needed to repair a fracture or defect site isoften not available in a thick enough form. While multiple fragments maytogether meet the size and shape requirements, several prominentconcerns have placed a practical limitation on the implementation ofthis concept. There is considerable uncertainty regarding the structuralintegrity provided by fragments positioned adjacent to one anotherwithout bonding or other means of securing the fragments to each other.Moreover, there is concern over the possibility that a fragment may slipout of position, resulting in migration of the fragment and possiblefurther damage in or near the area of implantation.

In addition, due to the geometry of bones such as the femur and tibia,all portions of the bones are not readily usable as a result of sizelimitations. Thus, prior art implants, specifically allografts, areproduced with an inefficient use of source bones.

There is a need for new, fundamental approaches to working with andprocessing tissues, in particular allograft material, especially withregard to machining, mating, and assembling bone fragments.Specifically, there is a need for an implant that allows more efficientuse of source material. More specifically, there is a need for animplant that is an integrated implant comprising two or more bonefragments that are interlocked to form a mechanically effective, strongunit.

SUMMARY OF THE INVENTION

The present invention is related to an implant including a body havingan inner sheath and at least one outer sheath. Each sheath is formedfrom a different bone and has an interior surface and an exteriorsurface. The exterior surface of each outer sheath contacts the interiorsurface of no more than one other outer sheath. In one embodiment, acore is disposed in the inner sheath and is formed from a bone otherthan the bones of the sheaths. The core can be formed of cancellousbone, while at least one sheath can be formed of cortical bone. Inanother embodiment, at least one sheath can be formed of cancellous boneand the core can be formed of cortical bone. The bones are at least oneof autograft, allograft, and xenograft bone tissue, and the bone tissueof at least one bone may be partially demineralized or demineralized. Ina further embodiment, the body is formed from a cross-section of thesheaths and core, with the cross-section including at least a portion ofeach sheath and core. The sheaths and core can be coupled together withat least one fastener that may intersect each of the sheaths and core,with the fastener being a screw, key, pin, peg, rivet, cotter, nail,spike, bolt, stud, staple, boss, clamp, clip, dowel, stake, hook,anchor, tie, band, crimp, or wedge. Also, the sheaths and core can bebonded together with a bonding agent. At least one sheath may be packedwith bone growth materials and may include alignment indicia. Theexterior surface may be separated from a portion of the interiorsurface.

At least one of the inner sheath, an outer sheath, and the core can beat least partially dehydrated to fit against a surrounding matingsurface. Furthermore, at least one of the inner sheath, an outer sheath,and the core can be at least partially dehydrated to fit within asurrounding inner sheath or outer sheath provided with a greatermoisture content.

Contacting surfaces of adjacent sheaths can be machined surfaces so thatthe contour of the contacting surfaces is about the same. The machinedsurfaces permit press-fitting of one sheath into another sheath. In someembodiments, the bones are selected from a femur, tibia, humerus,fibula, ulna, and radius.

At least one supplemental sheath having an interior surface and anexterior surface also may be included, with the exterior surface of eachsupplemental sheath contacting the interior surface of no more than oneother sheath and the interior surface of each supplemental sheathcontacting the exterior surface of no more than one other sheath. The atleast one supplemental sheath is formed of a material selected frommetals, alloys, ceramics, polymers, and composites.

The present invention is also related to an implant having a body formedfrom a cross-section of a core and a plurality of sheaths. Each sheathhas an inner surface and an outer surface, and at least two sheaths areformed from different bones. The outer surface of a first sheath hasabout the same contour as the inner surface of a second sheath so thatthe first and second sheaths mate together, and the cross-sectionincludes at least a portion of each sheath and core. The core may beformed from a bone other than the bones of the sheaths, and in oneembodiment the core is formed of cancellous bone and at least one sheathis formed of cortical bone. In another embodiment, at least one sheathis formed of cancellous bone and the core is formed of cortical bone.

Also, the present invention is related to an implant with a body thatincludes at least one sheath defining a hole, with a core fit therein.The body is formed from at least two different bones selected from afemur, tibia, humerus, fibula, ulna, and radius.

Furthermore, the present invention is related to an implant with a bodyhaving two outer annular members and at least one inner annular member.At least one of the annular members is formed from bone and the annularmembers are coupled together to create a central chamber. In oneembodiment, each annular member has at least one surface that ispress-fit with the surface of another annular member. The outsidediameter of the outer annular members may be smaller than the outsidediameter of the at least one inner annular member. The implant can besymmetrical about an innermost annular member, with the diameter of theimplant progressively decreasing from the innermost annular member toeach outer annular member. The central chamber can be packed with atleast one of bone material and bone inducing substances.

In one embodiment, at least one annular member is formed of cancellousbone and at least one annular member is formed of cortical bone. Aplurality of annular members may be coupled together with at least onefastener. Also, a plurality of annular members may be bonded togetherwith a bonding agent. In some embodiments, the annular members havenon-circular shapes, such as generally oblong shapes. At least onesupplemental annular member may be coupled to at least one of theannular members formed from bone, with the at least one supplementalannular member being formed of a material selected from metals, alloys,ceramics, polymers, and composites. At least one annular member mayinclude alignment indicia, and adjacent surfaces of at least two annularmembers may not completely contact each other.

The invention further relates to an implant with a body having at leasttwo ring-shaped members formed from bone that are coupled together tocreate a central chamber. The ring-shaped members may have ridges thatmate and press-fit together.

Another implant of the present invention includes at least two layers ofbone components coupled to each other, the components together definingat least one securing region, and at least one insertable securingelement adapted for placement in the at least one securing region. Theat least one securing region may be a recess or hole, and each layer maybe formed from a different bone selected from a femur, tibia, humerus,fibula, ulna, and radius. At least one layer may be formed of cancellousbone and at least one layer may be formed of cortical bone. Also, thelayers may include at least one of autograft, allograft, and xenograftbone tissue, and the layers may be bonded together with a bonding agent.The bone tissue of at least one bone may be partially demineralized ordemineralized, and the layers may be bonded together with a bondingagent. A first layer may be at least partially dehydrated to mateagainst at least one other layer. Adjacent layers may be provided withmutually contacting surfaces that are machined to have about the samecontour, and the contacting surfaces of adjacent layers may be press-fittogether.

In addition, the implant may further include at least one supplementallayer coupled to at least one of the layers of bone components, with theat least one supplemental layer being formed of a material selected frommetals, alloys, ceramics, polymers, and composites. Also, the implantmay further include a chamber packed with bone growth materials. In someembodiments, at least one layer includes alignment indicia, and theouter surface may be separated from a portion of the inner surface.

The present invention is further related to a hollow body having aminimum wall thickness, the body being formed from a plurality ofportions of bone sections with each section having a thick-walledportion and a thin-walled portion. The thick-walled portion has a wallthickness at least as thick as the minimum wall thickness, and thethin-walled section has a wall thickness less than the minimum wallthickness. Only thick-walled portions are coupled together to form thebody. The thick-walled portions are coupled together with at least oneportion having a first coupling and at least one portion having a secondcoupling, with the portions being joined together by interfittingtogether the first and second couplings. At least one coupling may be atleast partially dehydrated to mate against another coupling. In oneembodiment, the first coupling is a male coupling and the secondcoupling is a female coupling so that the portions are mated in amale-female relationship. The male coupling may be a tenon and thefemale coupling may be a mortise, or the male coupling may be a tongueand the female coupling may be a groove.

The present invention is also related to an implant including a layerformed of a first bone and at least one layer formed by a curablecarrier, with the at least one layer being molded to the first bone. Thelayer formed of a first bone may include a primary sleeve with a topsurface, a bottom surface, an inner surface, and an outer surface, withthe at least one layer of curable carrier being molded to the innersurface or the outer surface. In one embodiment, the curable carrierfurther includes bone or ceramic in powder, chips, or fibers. At leastone secondary sleeve may be provided, with each secondary sleeve beingcoupled to a primary sleeve or another secondary sleeve by a layer ofcurable carrier.

Additionally, the present invention is related to a method of forming animplant including: surrounding at least a portion of a bone section witha first mold to create a cavity therebetween; filling the cavity with afirst substance, and coupling the first substance to the bone section.The first substance may be at least one of a curable carrier, bonepowder, bone chips bone fibers, or ceramic, and be coupled to the bonesection by curing or by compaction.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the present invention are disclosed in theaccompanying drawings, wherein similar reference characters denotesimilar elements throughout the several views, and wherein:

FIGS. 1A to 1D show prior art exemplar bone sizes and shapes for bonesfrom an adult human;

FIGS. 1E–1F show prior art exemplar bone sections having varying wallthickness, the sections taken transverse to the longitudinal axis of thebones;

FIGS. 1G to 1I show perspective views of bone portions that may becombined to form an embodiment of an implant of the present development;

FIGS. 1J to 1K show perspective views of another embodiment of thepresent development combining multiple bone sections;

FIG. 2A shows a perspective view of the embodiment of FIG. 1K withsection lines;

FIG. 2B shows a perspective view of the section of the embodiment ofFIG. 1K forming an implant;

FIG. 2C shows a side view of the implant of FIG. 2B;

FIG. 2D shows an exploded view of the implant of FIG. 2B;

FIGS. 3A to 3C show perspective views of sections of a tibia and femurcombined in another embodiment of the present invention;

FIG. 3D shows a top view of the embodiment of FIG. 3C;

FIGS. 4A to 4D show top views of yet another embodiment of the presentinvention combining sections of bone having acceptable wall thicknesswith mating joints;

FIGS. 4E to 4G show exploded, perspective views of another embodiment ofthe present invention combining sections of bone having acceptable wallthickness with mating joints;

FIGS. 5A to 5E show perspective views of additional embodiments of thepresent invention combining multiple bone sections;

FIG. 5F shows an exploded, perspective view of another embodiment of thepresent invention combining multiple bone sections;

FIG. 6A shows a top view of another embodiment of the present inventionforming a femoral ring implant;

FIG. 6B shows a side view of the implant of FIG. 6A;

FIG. 6C shows a cross-section of the implant of FIG. 6A taken along lineVIC—VIC;

FIG. 6D shows a cross-section of the implant of FIG. 6A taken along lineVID—VID;

FIG. 7A shows perspective views of concentric rings formed of bonematerial for coupling to form an implant;

FIG. 7B shows a side view of an embodiment of the present invention withan implant formed from the concentric rings of FIG. 7A;

FIG. 7C shows an exploded, perspective view of the implant of FIG. 7B;

FIGS. 8A and 8B show exploded, side views of another embodiment of thepresent invention forming a spacer;

FIGS. 8C and 8D show additional side views, respectively, of bone piecesof the spacer of FIGS. 8A and 8B;

FIG. 8E shows a side view of the teeth used in the spacer of FIGS. 8Aand 8B;

FIGS. 9A to 9C show exploded, perspective views of additionalembodiments of the present invention using washer-shaped bone portions;

FIG. 10 shows a top view of an additional embodiment of an implantaccording to the present invention with bowed bone portions;

FIG. 11 shows a perspective view of an additional embodiment of animplant according to the present invention with press fitting of boneportions in two locations;

FIG. 12 shows an exploded, perspective view of an additional embodimentof an implant according to the present invention with bone portions thatmate;

FIG. 13 shows a top view of an additional embodiment of a multilayerimplant according to the present invention;

FIG. 14 shows an exploded, perspective view of the implant of FIG. 13;

FIG. 15 shows a perspective view of an embodiment of the presentinvention formed with a cancellous body and cortical struts;

FIG. 16 shows an exploded, perspective view of an additional embodimentof the present invention formed with a cancellous body and corticalstruts;

FIG. 17 shows an exploded, perspective view of an additional embodimentof the present invention formed with a combination of cancellous andcortical bone;

FIG. 18 shows a perspective view of an additional embodiment of thepresent invention formed with a combination of cancellous and corticalbone; and

FIGS. 19A and 19B show perspective views of the formation of a compositeimplant by molding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Any of a wide variety of different implant structures, particularlyallograft, autograft, and/or xenograft implant structures, can beprepared according to the teachings of the present invention. While arepresentative selection of implant structures are described anddepicted herein, additional disclosure is found in U.S. ProvisionalApplication No. 60/191,099 filed Mar. 22, 2000, which is herebyincorporated herein in its entirety by reference, including all figures.

The present invention allows a more efficient use of bone sections, bypermitting those sections that would otherwise have been rejected due toinsufficient wall thickness to instead be incorporated in a compositebone section. The composite implant is created by taking two or morebone sections and combining them to create a greater wall thickness.Some or all of the natural shape of each bone may be retained.Furthermore, the composite may be formed of a shape appropriate forimplantation, or instead may be formed of a shape that is suitable asbone stock for eventual fashioning into a particular implant or forms.

As used in the description of the present invention, the words fitting,interfitting, mating, locking, interlocking, meshing, and interlacingare all used generically to describe the joining of bone sections orpieces together. Thus, these words are not limited to the use of anyparticular manner of joining. Thus, for example, the press-fitting ofone bone section within a cavity formed in another bone section may bedescribed using any of the above-mentioned terms. In addition, althoughvarious preferred mechanical fastening approaches are described, thepresent invention allows the use of any mechanical device for joiningtwo or more separate parts of an article or structure. Such mechanicaldevices include, but are not limited to the following: screws, keys,pins, pegs, rivets, cotters, nails, spikes, bolts, studs, staples,bosses, clamps, clips, dowels, stakes, hooks, anchors, ties, bands, andcrimps. Also, bonding agents or other chemical means for joining twoseparate parts may be employed alone or in combination with themechanical devices. Thus, as appropriate, the means disclosed herein forfixing bone sections to each other may be substituted, as with theabove-mentioned mechanical devices, bonding devices, or chemical means.Furthermore, although particular types of joints are disclosed, thepresent invention is directed to the creation of implants that may bejoined using other joints.

While the present invention is preferably directed to the creation ofimplants from allograft material, the present invention may also beapplied to implants that utilize other materials, including but notlimited to the following: xenograft, autograft, metals, alloys,ceramics, polymers, composites, and encapsulated fluids or gels.Furthermore, the implants described herein may be formed of materialswith varying levels of porosity, such as by combined bone sections fromdifferent bones or different types of tissue having varying levels ofporosity. For example, cancellous bone is available in a range ofporosities based on the location in the body from which the bone isharvested. Extremely porous cancellous bone may be harvested fromvarious areas such as the iliac crest, while less porous bone may beharvested from areas such as a tibial condyle. Thus, the materialsproperties—particularly the porosity—of the bone components may beselected to meet the needs of a given application.

Cancellous bone components may be attached to syringes or aspirators,and blood or other fluids such as bone-growth inducing substances may bedrawn into the plugs. The use of mechanically applied pressure, such aswith aspiration devices, permits a greater degree of fluid absorptionand/or concentration to be achieved than otherwise readily obtainable bysoaking bone in such fluids without applying pressure from a device. Inembodiments of the present invention that include hollow regions, a plugof cancellous bone formed using the aforementioned technique may beinserted therein. Alternatively, the plugs may be soaked in a suitablefluid.

Also, the implants described herein may be formed of bone materials withvarying mineral content. For example, cancellous or cortical bone may beprovided in natural, partially demineralized, or demineralized states.Demineralization is typically achieved with a variety of chemicalprocessing techniques, including the use of an acid such as hydrochloricacid, chelating agents, electrolysis or other treatments. Thedemineralization treatment removes the minerals contained in the naturalbone, leaving collagen fibers with bone growth factors including bonemorphogenic protein (BMP). Variation in the mechanical properties ofbone sections is obtainable through demineralization. Advantageously,use of a demineralizing agent on natural bone transforms the propertiesof the bone from a stiff structure to a relatively pliable structurewhen it is hydrated. Some portions of interfitting bone components maybe demineralized in order to achieve improved interfitting. For example,a tissue form may include two bone components having portions that arecoupled together with an interference fit. The interference fit may beenhanced if the surface region of one or more of the components isdemineralized so that it is pliable and exhibits some elasticity and/ormalleability.

In addition, while many of the embodiments described herein show bonecomponents disposed at right angles, or joints formed with right angles,angles that are greater or less than ninety degrees may alternatively beused in implants of the present development.

FIG. 1G shows a first embodiment of implant 16 having an outer sheath17, an intermediary sheath 18, and a core 19. It should be noted thatwhile bone sections described herein are referred to as sleeves, thesecomponents need not be cylindrical or otherwise symmetrical. In thisembodiment, outer sheath 17 is a bone section, for example of a femur,that has the outer surface or contour naturally found on a femur. Thus,the outer surface 20 of outer sheath 17 does not require machining andis not machined. The inner surface 21 of outer sheath 17 has beenmachined to a particular configuration so that intermediary sheath 18fits within outer sheath 17. Alternatively, as shown in FIG. 1H, implant16 may have a through hole 22 instead of a core 19, creating a cavity inimplant 16. If a through-hole is provided instead of core 19, a hollowimplant may be created and bone growth materials such as bone materialsin the form of chips, slurries, or fibers, as well as bone inducingsubstances can be provided therein. While the cavity may be formed fromsleeves with two open free ends, such a hollow region may also becreated by incorporating one or more sleeves with one free end closed.It should be noted that two or more sections of bone are used to createthe composite, and thus there is no limit to the number of sheaths orbone sections that may be combined. Typically, insert or core 19 iscylindrical in shape, as shown in FIG. 1I, and may be made of cancellousbone while each surrounding sheath may be made of cortical bone.Alternating layers of cortical and cancellous bone may be used, orseveral layers of the same type of bone may be used along with adifferent type of bone.

The components that are used to create implant 16 may all be formed fromcortical bone, all from cancellous bone, or a combination of componentsformed from cortical and cancellous bone. The interfitting of thecomponents may be achieved through a variety of means, including but notlimited to the following: pinning, bonding with a suitable bone bondingagent or chemical means, press fitting, threadably engaging (as byhelically screwing one component into another), inserting a taperedcomponent into a component with a matching inner surface, twist-locking,or other interlocking means such as will be described in otherembodiments. While the present development preferably allows thecreation of an implant 16 from all bone material, it is also anticipatedthat one or more components used to create implant 16 may be formed ofnon-bone material such as a synthetic or other material.

As shown in FIG. 1J, in a second embodiment of the present inventionmany types of bones may be combined in layers to form bone stock 25′. Aradius 13 may be encased in humerus sleeve 12, which may be encased intibia sleeve 11, which may further be encased in femur sleeve 10 thatretains the original outer shape of the femur. In alternate embodiments,other bones may be used, such as a fibula or ulna. By machining theinner and/or outer surfaces of each bone section, the bone sections maybe inserted into each other with an interfitting relationship. This mayresult in a strong press-fit, but additional or alternate means offixation may be employed, such as mechanical means.

The moisture content of the bone sections also may be varied toadvantageously permit improved interlocking. Bone sections initially maybe provided with moisture content as follows: (1) bone in the naturalstate fresh out of the donor without freezing, (2) bone in the frozenstate, typically at −40° C., with moisture content intact, (3) bone withmoisture removed such as freeze-dried bone, and (4) bone in the hydratedstate, such as when submersed in water. The expansion and contractionproperties that can be obtained from bone during heating, cooling,dehydrating, and hydrating permit an alternate approach to achieving atight press-fit. In addition, the use of such approaches can provide atighter press-fit than otherwise obtainable, as well as loosen themanufacturing tolerances required for mating sections of bone.

For example, in the embodiment shown in FIG. 1J, sleeve 12 is initiallysupplied with a first outer diameter and a first inner diameter.Subsequent freeze-drying of sleeve 12 results in shrinkage such thatsleeve 12 assumes a configuration with a second outer diameter that issmaller than the first outer diameter, while having a second innerdiameter that is smaller than the first inner diameter. When sleeve 12is rehydrated or treated with a swelling agent, sleeve 12 may reassume aconfiguration with the first outer diameter and first inner diameter. Byproviding a bone section such as a sleeve 12 in the freeze-dried statewhile disposed inside another bone section such as sleeve 11 that may beloosely interference fit, rehydration of sleeve 12 in place permits atighter interference fit to be achieved. Notably, a bone section such ascore 13 has no inner diameter, and thus such a bone section may shrinkin outer diameter only when freeze-dried. Thus, similarly, core 13 maybe the bone section that is rehydrated to provide a tighter mating andinterference fit with a sleeve 12. Use of these properties can permitgreater variation in dimensional tolerance between bone sections duringmanufacture, while tight final assembly can still be achieved. Inaddition, protrusions on bone sections become smaller when dehydrated,but expand when rehydrated; in contrast, recesses in bone sectionsbecome smaller when hydrated, but larger when dehydrated. Temperaturechanges may also be used to achieve better interference fits.

Turning to FIGS. 1J–K, a hole 23 of similar dimension may be created ineach bone section, and when the holes are aligned to be coaxial, a pin24 may be inserted in the holes 23 for fixation. Alternatively, the bonesections may have a slot formed therethrough, similar in orientation topin 24, and a key can be inserted or press-fitted into the slot to fixthe sections with respect to each other. Other bones may also be used,for example an ulna (lower arm) is similar in configuration to radius13, and thus may be readily substituted. In addition, a fibula can alsobe readily used in some embodiments, accounting for the size of the boneand any required machining. Also, although the embodiment shown in FIGS.1J and 1K show bones with generally cylindrical shapes, other shapes canbe used, for example by machining the bones to have a rectangular shapeor any other shape.

Bone stock 25′ is preferably solid, and formed by fitting a smallerdiameter bone core within at least one larger diameter sheath. Thus, theavailability of precisely machined cores and sheaths permits bone stock25′ to be sized according to the application or anatomy encountered inany given situation. In addition, implants may be constructed from asupply of standardized core and sheath sizes or bone stock sizes so thatany required wall thickness can be obtained. The ability to createcomposite implants of varying sizes has widespread use, particularly inapplications such as femoral ring allografts which can benefit fromincreased wall thicknesses.

In alternate embodiments of bone stock 25′, components havingnon-circular shape may be provided, although not necessarily the naturalshape of the original bone. For example, an outer sheath can mate withan inner sheath which has a generally triangular shape, with the insidesurface of the outer sheath geometrically conforming to the outsidesurface of inner sheath. Other polygonal shapes are also contemplated,including parallelograms such as rectangles. In addition, a core may beprovided with a shape distinct from both the cylindrical outside surfaceof the outer sheath and the outside surface of the inner sheath. Thus,the present development permits components with varying outside surfaceshapes to be interfit to create an implant.

The availability of larger bone stock, as by combining several bonesections, makes it possible to create implants that are properlyconfigured for implantation during a wide variety of procedures. Forexample, anterior interbody fusion is a surgical procedure whichreplaces some or all of a disc with a bony graft (implant) by using ananterior approach to the disc. Such a procedure is typically employed inthe cervical spine, and implantation of an implant is an effectivemodality for the treatment of such conditions as degenerative discdisease and herniated nucleus pulposus (slipped disc). Anteriorinterbody fusion is also used in the lumbar spine in cases ofunsuccessful posterior approaches, or in procedures directed todestroyed or damaged facet joints, procedures that combine posteriorinstrumentation with an anterior discectomy (i.e. removal of herniateddisc material from the spinal canal so that the spinal cord or nerve isrestored to an unpinched state) and fusion (which allows vertebrae toeffectively be knit together into a solid bony mass), along with otherprocedures that cannot employ a posterior approach. Thus, the implantsmay also be employed in anterior discectomy and fusion, which involvesthe removal of an intervertebral disc and the replacement of that discwith an implant that will undergo fusion, both steps being undertakenvia an anterior approach. Other surgical procedures employing theanterior approach, including procedures used in fusing the thoracicregion, may also make use of the implants.

Alternatively, surgical procedures involving a posterior approach mayalso employ the implants created using the current invention. Forexample, posterior lumbar interbody fusion, another surgical techniqueused for spinal fusion, involves the posterior insertion of an implantinto the intervertebral space following posterior excision of a discthrough the spinal canal.

Bone stock 25′ as shown in FIGS. 1J and 1K may be sectioned, forexample, as shown in FIGS. 2A–2D, along axes 43 and 44, resulting in across-section slice 45 of bone stock 25′ having a thickness X₅ as shownin perspective view in FIG. 2B and in side view in FIG. 2C. In thisembodiment, a pair of pins 24 instead is used to retain the pieces ofbones 10, 11, 12, and 13 in engagement. Pins 24 may be oriented at anangle with respect to each other, as shown in FIG. 2C, such that theyare nonparallel, thereby resisting separation of the bone pieces.Alternatively, the pieces of bone may be keyed (not shown) foradditional interlocking. Such composite bone stock may be used, forexample, to create an implant suitable for posterior lumbar interbodyfusion. Optionally, in order to prevent migration of such an implantwhen placed in an anatomical region, serrated regions in the form of sawteeth 24′ may be provided on the periphery of slice 45. Although slice45 includes a core 13 that is fully surrounded by sleeve 12, as shownfor example in the exploded view of slice 45 in FIG. 2D, alternateembodiments of a slice of bone stock 25′ do not completely surround core13.

While bone stock 25′ utilizes four separate bone pieces, other numbersof pieces are contemplated. For example, a core may be surrounded byonly two sleeves to produce a desired stock size. Also, pins 24 may beformed from bone.

Another composite implant is shown in FIGS. 3A–3D. In this embodiment, asection of a femur 46 has a inner surface 47. Preferably, in order toincrease the wall thickness of section 46, this bone section may be usedas a sleeve that surrounds a portion of a tibia section 48. Although thetibia naturally has a generally triangular shape, a portion 49 of thetibia 48 may be machined to have an outer geometry that mates with innersurface 47 of femur 46. A canal 50 may remain in the composite implant,or it may be filled with another bone or other material. By insertingportion 49 within sleeve 46, a protruding section 52 remains on tibiasection 48. Such a section may be cut off, for example along axis 51, sothat section 52 may be used for another purpose, such as serving as bonematerial for use in other implants.

Yet another approach to maximizing the use of a bone sections with thinwall areas is shown in FIGS. 4A to 4D. In this embodiment, a femursection 53 is cut with a tongue and groove pattern, creating a portion54 having an acceptable wall thickness and a portion 55 with anunacceptable wall thickness. A similar cut is performed on another femursection, and the portion 55 from the second femur section may be removedand matched with the portion 54 from the first femur section. Thus, acomposite implant is created with consistently thick and acceptable wallthickness. Portion 53 may be used for another purpose. In addition tomatching tongues 56 and grooves 57 formed in sections 55 and 54,respectively, other matching geometrical shapes such as matching notches58 may also be provided as shown in FIG. 4E. Other suitableconfigurations of interlocking portions include interlocking teeth 59formed in matching sections 54′ and 55′, as shown in FIGS. 4F and 4G. Inan alternate embodiment, a synthetic portion may be matched with a boneportion to create a composite implant with appropriate wall thickness,and may be formed of other materials such as metals, polymers, orceramics.

FIGS. 5A to 5C show implants created by joining three components.Implant 60 has two outer portions 61 and 62 that surround thecylindrical surface 63 of core 64. Outer portions 61 and 62 are joinedto each other using pins 65 and 66 (shown in phantom), and core 64 ispress fit or otherwise secured between portions 61 and 62. In theembodiment shown in FIG. 5A, portions 61 and 62 have mating surfacesdefined at areas 67 and 68 that do not interfit. Alternatively, as shownin FIG. 5B, implant 69 has two outer portions 70 and 71 that interfitand surround a core 64. Portion 70 has a tongue portion 72 that fits ina groove in portion 71. Likewise, portion 71 is also provided with atongue portion 73 that fits in a groove in portion 70. Notably, designsemploying tongue and groove configurations have a significantlyincreased mating surface area, thereby providing a greater surface overwhich joining can be achieved with concomitantly greater strength.

Interfitting may also be achieved using the design of implant 74 shownin FIG. 5C. Portion 75 has protruding portions 76 and 77 that each arepartially formed with outside surface 78, while portion 79 hasprotruding portions 80 and 82 that interfit with protrusions 76 and 77.As shown in FIG. 5D, implant 84 may instead include a combination oftongue portions 86 and 88 that fit within grooves disposed in opposingouter portions, protruding portions 90 and 92, as well as matingsurfaces 94 and 96. Implant 98 uses dovetail joints 100 to secure outerportions 102 and 104. The dovetail joint is particularly useful becauseit resists pullout, although sliding may still occur along axis 106. Thedovetails provide a positive lock transverse to axis 106 so that pulloutcan be prevented, and such an interlocking arrangement of componentsgenerally resists the separation of the bone components from each other.As with the tongue and groove design, the use of a dovetail jointcreates a greater surface area for bonding. Although implant 98 is shownwith only one dovetail on each outer sheath portion, additionaldovetails may be provided. Additionally, the present development allowsthe joining of more than two outer portions. Thus, instead of twohalves, three or more outer portions may be joined. Furthermore, thecore may be of any desired shape, as may be the outside surface of theouter portions. Portions of the implants, such as portions 75 and 79,may be formed of different materials, for example cortical bone,cancellous bone, and ceramic materials.

Numerous types of joints are useful in the present development,including joints that permit articulation such as a ball and socket typeof joint, and particularly joints that permit firm interlocking betweentwo components to prevent relative movement between the components.Preferably, mortise and tenon joints can be used to interfit multiplebone components to create an implant as shown for example in FIG. 5F.Bone component 122, shown in exemplary form with a rectangular shape,contains a rectangular mortise or cavity 124. Bone component 126, alsorectangular in overall configuration, includes a rectangular-shapedtenon 128 that is inserted in cavity 124 to thereby form a joint. Thesize and shape of tenon 128 is closely matched to that of cavity 124.Once components 122 and 126 are joined, as shown by arrow A, an implantor larger bone stock is created. The mortise may be partial or extendthrough the component, and a tenon sloped haunch portion may be providedon the tenon for interfitting with a mortise sloped haunch portion onthe mortise. Other forms of the mortise and tenon joints are alsoappropriate, as are other coupling arrangements such as edge jointsincluding tongue and groove joints, rabbeted joints, toothed joints, anddovetail joints.

The use of insertable securing elements such as keys, pegs, pins,wedges, or other suitable components in joints to assist in securingbone components to each other is also an effective approach to providinga stable joint. Keys, for example, may be inserted in notched or groovedareas in bone components, serving as the securing element between two ormore bone components. Parameters that may be varied when usinginsertable securing elements, such as keys, include the angle ofapplication, the spacing of the elements, and the thicknesses of theelements.

Referring to FIGS. 6A–6D, a femoral ring implant 200 is shown for use inanterior lumbar interbody fusion, and is formed of several layers ofbone in the form of sleeves. In the preferred embodiment, a sleeve 202formed from a femur or tibia has another sleeve 204 formed from ahumerus inserted therein. The sleeves 202, 204 may be press-fit, pinned,keyed, and/or joined by other means. Although implant 200 is shown witha central chamber 206, which may be left empty or filled with bonematerials or other bone inducing substances, in alternate embodimentscentral chamber 206 may be filled with another bone portion to create asolid implant. A cancellous plug, for example, may be placed in centralchamber 206. Combinations of cortical or cancellous bone may be used,and additional sleeves may also be provided. Saw teeth 208 or otherprotrusions may be provided on the periphery of implant 200 to anchorthe implant in the desired anatomical region. Implant 200 is formed in agenerally kidney-shaped configuration to conform to the natural anatomyof vertebral bodies encountered during anterior lumbar interbody fusion.

Alignment indicia 210 may be provided on the outer surface of implant200, as with a line or other aid. Preferably, indicia 210 is an imprint,i.e. with ink, although indicia 210 may instead be provided in the formof surface scoring. The indicia suitable for the present inventionincludes, but is not limited to, markers such as lines, arrows,lettering, and symbols. In addition, alignment indicia 210 preferably isprovided on the anterior side of implant 200 to aid in alignment withthe natural anatomy encountered during surgery, and particularly to aidin alignment with the anterior longitudinal ligament (ALL) that extendsover the length of the lumbar spine anterior to the vertebral bodies. Inparticular, the ALL may be used as a landmark in combination withalignment indicia 210, for example, to permit a surgeon to properlyalign implant 200 with respect to surrounding anatomy.

Referring to FIGS. 7A to 7C, interlocking concentric circular bonecomponents may also be created from bone stock. For example, concentricbone portions 1020, 1022, 1024, 1026, and 1028 may be combined to forman implant. Some of the concentric circular components may be providedwith two portions, each having a different outer diameter such asportion 1047 and ridge 1048. Ridge 1048 has an outer diameter that isslightly smaller than the inner diameter of ridge 1049, thus allowingridge 1048 of a first component to be press fit into the ridge 1049 of asecond component. This permits implants of varying sizes to be createdby interlocking several bone components together, for example to createimplant 1050. Side and exploded, perspective views of implant 1050 areshown in FIGS. 7B and 7C respectively. Keys may also be inserted intothe walls of assembled bone components to provide further interlockingof the concentric cylinders. Furthermore, once assembled and secured toeach other, the annular members may be cut to create other appropriateshapes. Implant 1050 utilizes bone portions that are formed from thenatural size and overall geometry of particular bones, so that availablebone material may be used efficiently. For example, bone portions 1020,1028 may be formed from a radius, bone portions 1022, 1026 may be formedfrom a humerus, and bone portion 1024 may be formed from a femur.Although implant 1050 is shown with concentric circular portions, isother embodiments non-circular, ring-shaped bone components may also besimilarly provided such as oblong arcuate forms like elliptical shapes,or polygonal shapes. In some embodiments, caps are optionally providedin the outermost concentric circle bone portions to form acompletely-enclosed chamber within implant 1050.

Turning to FIGS. 8A–E, another spacer implant 1100 according to thepresent invention is shown. Two bone pieces 1102, 1104 are provided withmating portions 1107, 1108 respectively. Once interfitted, bone pieces1102, 1104 provide a multi-layer, oval-shaped implant structure with acentral hole 1112, which may be packed with bone-growth inducingsubstances. Preferably, one or more of the outer surfaces on implant1100, such as outer surface 1106, is provided with teeth 1110. In apreferred embodiment, teeth 1110 are pyrimidal in shape with edgesformed at an angle β of about 60°. Preferably, at least a portion of aninner surface of a bone piece 1102, 1104 is provided with a protrusionthat is received in an opposing groove. For example, as shown in FIGS.8A and 8B, bone piece 1102 is provided with an inner surface thatincludes a groove 1118 for mating with a symmetrically formed protrusion1116 on bone piece 1104. Centering lines 1114, 1116 may also be providedon implant 1100 to assist in the orientation and overall placement ofimplant 1100 in the body. Although the implant 1100 of FIGS. 8A–E isformed of two layers of bone, implants of more than two layers ofinterfitting bone are contemplated.

Referring to FIGS. 9A–C, various other configurations of bone portionsmay be provided. For example, an implant 1200 may be formed withinterfitting washer 1202 and base 1204 bone pieces. Alternatively, animplant 1220 may be formed with multiple washer-like pieces 1222, 1224that interfit with a core 1226. In addition, an implant 1240 may beformed with washer-like pieces 1242, 1244, an intermediate piece 1246,and a core 1248 that extends the length of all pieces 1242, 1244, 1246.The mating surfaces of the components of these embodiments may be fixedto each other using any of the aforementioned means such as pins andadhesives. In addition, different types of bone may be selected for thecomponents of these embodiments. In one embodiment, implant 1200includes a cancellous ring 1202 and a cortical base 1204. In anotherembodiment, implant 1240 includes cortical washer-like pieces 1242,1244, a cancellous intermediate piece 1246, and a cortical core 1248.

Another embodiment according to the present invention is shown in FIG.10. Implant 1260 is formed with bowed bone portions 1262, 1266. Boneportion 1262 is provided with grooved regions 1264, while bone portion1266 is provided with protrusions 1268 that mate with grooved regions1264.

Yet another embodiment of an implant 1280 is shown in FIG. 11. An outerbone portion 1282 surrounds an inner bone portion 1284. Advantageously,inner bone portion 1284 only contacts outer bone portion 1282 along twosmall regions 1286, 1288 along the length of portions 1282, 1284. Thus,in this embodiment a press-fit of bone portions 1282, 1284 is onlyprovided at regions 1286, 1288. Such a construction permits outer boneportion 1282 to deflect with respect to inner bone portion 1284. Such aconstruction facilitates press-fitting of outer and inner bone portions.Closely mating outer and inner bone portions may be difficult topress-fit due to the tightness inherent in the fit itself and thedimensions of the bone portions. A less tight fit, as provided forexample by implant 1280, may permit a press-fit to be achieved with lessdifficulty. In sum, an implant 1280 with an inner bone portion 1284 ofoblong or slightly elliptical geometry can provide an acceptableinterference fit, while facilitating assembly without as much concernfor breakage. While a press-fit with two points or regions of contacthas been described, it is also contemplated that press-fits with morethan two points or regions of contact may be used.

Further embodiments of multipiece implants are shown in FIGS. 12–14.Referring to FIG. 12, implant 1300 is formed of bone portions 1310,1312, and 1314. Bone portion 1310 includes a central hole or recess 1316with a diameter D₁, while bone portion 1312 includes a prong 1320 with adiameter D₂ and a central hole or recess 1318 with a diameter D₃.Diameters D₁, D₂ are chosen such that bone portions 1310 and 1312 mateat hole 1316 and prong 1320, and preferably a press-fit is achieved.Similarly, bone portion 1314 includes a prong 1322 with a diameter D₄and a central hole or recess 1324. Diameters D₃, D₄ are chosen such thatbone portions 1312 and 1314 mate at hole 1318 and prong 1322, andpreferably a press-fit is achieved. In the embodiment shown, diametersD₂, D₄ are chosen to be different. Thus, if an implant requires acentral cancellous bone portion 1312 between cortical bone portions1310, 1314, the proper construction is more likely to be achieved due tothe specific interfitting relationships of the bone portions.

As shown in FIGS. 13–14, a multi-layer implant 1330 includes a core boneportion 1332 surrounded by bone portions 1334, 1336, 1338, 1340. Theshape of core bone portion 1332 serves as a key for orienting and matingwith bone portions 1334, 1336, and similarly bone portions 1334, 1336together serve as a key for orienting and mating with bone portions1338, 1340. Any number of bone portions may be aligned with respect toeach other using this key configuration.

Referring now to FIGS. 15–16, the use of cortical bone struts to conferadditional structural strength to implants is shown. For example,implant 1350 of FIG. 15 includes a cancellous body 1352 with holes 1353formed therein. Cortical struts 1354 are inserted in holes 1353 toimprove the strength of implant 1350. In particular, because cancellousbone does not provide significant structural strength, cortical strutswith higher structural strength, particularly in compression, are used.Advantageously, implant 1350 is formed in part from an osteoconductivematerial, the cancellous bone, to facilitate incorporation of theimplant into surrounding bone tissue. Implant 1350 may be formed of bonethat is demineralized, partially demineralized, or with natural mineralcontent, and may be formed from other shapes. Holes 1353 and struts 1354may have other cross-sections such as triangular or rectangular shapes,and similarly body 1352 may be another shape. A central hole 1355 alsomay be included and additional materials may be packed or moldedtherein. Turning to FIG. 16, an exploded view of an implant 1360 isshown. Implant 1360 includes cortical end caps 1362, 1364 disposed onopposing sides of body 1368. Cortical struts 1366 extend through holes1370 in body 1368 to improve structural integrity of the implant. One orboth of end caps 1362, 1364 may include holes or recesses, such as holes1372 as shown in end cap 1364, to receive portions of struts 1366. Thestruts may be press-fit within holes 1370, 1372. Cortical end caps 1362,1364 also serve to distribute loading on implant 1360.

Additional embodiments of implants with combinations of cortical andcancellous bone are shown in FIGS. 17–18. Implant 1380 includes opposingcortical caps 1382 each with heads 1384 and protrusions 1386. Cancellousbody 1390 includes opposing recesses or holes 1390, which receiveprotrusions 1386 of caps 1382. Implant 1392 includes cortical shells1394, 1396 with a cancellous body 1398 disposed therebetween. A centralregion 1399 may be empty, filled with a plug of bone material such ascancellous bone, or filled with other materials.

Implants may be formed from composites of bone material and materialthat is molded thereto. For example, femur section 46 shown in FIG. 3Ahas an inner surface 47 that conforms to the natural shape of the femurbone canal. The wall thickness of femur 46 varies, and may be increasedusing several approaches. As shown in FIGS. 19A and 19B, a moldingapparatus 1400 may be used to produce an implant 1410 with desired wallthickness. A mold 1402 or object of smaller dimension than the hole 1404defined by inner surface 47 of femur section 46, and a curable liquid,slurry, paste, or gel such as bone cement, a viscous polymer, or aceramic slurry can be poured between mold 1402 and inner surface 47 andallowed to set in place. Alternatively, or in addition, a mold 1406 witha larger dimension than femur section 46 may be placed around it. Thewall thickness of femur section 46 may be increased by pouring bonecement between mold 1406 and outer surface 1408, so that the bone cementextends from the top surface 1407 to the bottom surface 1409. Inalternate embodiments, the bone cement may not extend to top surface1407.

Once the bone cement has set, molds 1402, 1406 may be removed, leaving atissue form 1410 with a composite wall of the original femur section 46and bone cement sections 1412, 1414. Other filler materials can be usedwith molds 1402, 1406, such as a mixture of hydroxyapatite and cementthat sets in place. In alternate embodiments, materials are molded onlyto portions of bone sections, instead of being molded to completelysurround inner and/or outer surfaces of bone sections. Additional moldscan be used for surrounding adjacent bone sections in implants formedwith multiple pieces of bone, thereby permitting multiple bone sectionsto be coupled together with an intermediary layer of bone cement.

Molded sections such as sections 1412, 1414 may include mixtures orsuspensions of cancellous and/or cortical bone powder, bone chips, andbone fibers, in natural or demineralized conditions, in combination withbonding agents such as bone cements, water, fat, blood, thrombin, andfibrin. The fibers, in particular, may be oriented to provide particularmechanical properties. For example, fibers may be oriented generallyparallel to axis 1416, transverse to axis 1416, or in mixed orientationsin order to achieve desired strength when encased in bone cement that iscured. Other materials also may be combined with bonding agents or othercarriers, such as hydroxyapatite. Furthermore, sections 1412, 1414 mayadditionally be formed by applying pressure while curing occurs.

Alternatively, compactable powders and/or fibers of various sizes andshapes may be pressed and compacted in place, without bonding agents orwith minimal use thereof. Such pressed structures may be furtherencapsulated in thin layers of bone cements or polymers such asbiodegradable polymers. While loose powder of varying particle sizes maybe compressed and densified to produce a compact of the powder, it isdifficult to apply uniform pressures while producing the compact. Theso-called “single action” pressing technique, which typically applies aforce to the powder in a single direction, may be used in the presentinvention. However, in some embodiments, because it is desirable toproduce a compact with a more uniform density throughout the structure,other pressing techniques may be used.

Furthermore, the components of the implants described herein may beformed by molding various materials onto support structures such asmeshes or other structures that are known to one skilled in the art. Forexample, titanium mesh indicated for reinforcement of bony regions inorthopedic procedures is typically available in preformed round andoval-shaped cylinders. The metal mesh may be encapsulated or otherwisesurrounded by another material such as bone powder or bone fiberimpregnated bone cement that has dried in place around the mesh.Multiple bone components may be interfitted together and furtherencapsulated or otherwise surrounded by molded materials for additionalreinforcement. Also, molded material may be used to further couple twoor more pieces of bone together. For example, a polymer such aspolymethylmethacrylate may be placed in the central chamber of animplant and allowed to cure in place.

While various descriptions of the present invention are described above,it should be understood that the various features can be used singly orin any combination thereof. The various types of joints and connectionscan be used on bone implants or bone stock of different size orconfiguration, such that the invention is not to be limited to only thespecifically preferred embodiments depicted in the drawings.

Further, it should be understood that variations and modificationswithin the spirit and scope of the invention may occur to those skilledin the art to which the invention pertains. For example, multiple,differently shaped and sized bone portions can be constructed forinterfitting or interconnection to form a multiple part bone implantthat serves the desired purpose. Accordingly, all expedientmodifications readily attainable by one versed in the art from thedisclosure set forth herein are within the scope and spirit of thepresent invention and are to be included as further embodiments. Thescope of the present invention is accordingly defined as set forth inthe appended claims.

1. A method of forming a composite implant comprising: pouring a firstsubstance between a harvested natural occurring bone sleeve and a firstmold surface, the sleeve comprising a top surface, a bottom surface, anda wall extending therebetween wherein the wall forms an inner surface ofthe sleeve, the first substance contacting the wall along a portionthereof and extending partially from the bottom surface to the topsurface; allowing the first substance to bond to the sleeve and cure toform a composite; disengaging the first mold surface from the composite.2. The method claim 1, wherein the first substance comprises a viscouspolymer.
 3. The method of claim 2, wherein the first substance furthercomprises a ceramic filler material.
 4. The method of claim 1, whereinthe sleeve comprises an outer surface, and the first substance furthercontacts the outer surface.
 5. The method of claim 1, wherein the bonesleeve is partially demineralized or demineralized.
 6. The method ofclaim 1, wherein the bone sleeve comprises allograft bone.
 7. A methodof forming a composite implant comprising: pouring a first substancebetween a bone sleeve and a first mold surface, the sleeve comprising atop surface, a bottom surface, and a wall extending therebetween whereinthe wall forms an inner surface of the sleeve, the first substancecontacting the wall along a portion thereof and extending partially fromthe bottom surface to the top surface; pouring a second substancebetween an outer surface formed by the wall of the bone sleeve and asecond mold surface; allowing the first substance to bond to the sleeveand cure to form a composite; allowing the second substance to bond tothe sleeve; disengaging the first mold surface from the composite; anddisengaging the second mold surface from the second substance.
 8. Amethod of forming a composite implant comprising: pouring a firstsubstance between a bone sleeve and a first mold surface, the sleevecomprising a top surface, a bottom surface, and a wall extendingtherebetween wherein the wall forms an inner surface of the sleeve, thefirst substance contacting the wall along a portion thereof andextending partially from the bottom surface to the top surface; pouringa second substance between an outer surface formed by the wall of thebone sleeve and a second mold surface; allowing the first substance tobond to the sleeve and cure to form a composite; allowing the secondsubstance to bond to the sleeve; disengaging the first mold surface fromthe composite; and disengaging the second mold surface from the secondsubstance, wherein the bone sleeve, first substance, and secondsubstance together form an implant with a generally uniform wallthickness.
 9. A method of forming a composite implant comprising:pouring a first substance between a bone harvested natural occurringsleeve and a first mold surface, the sleeve comprising a top surface, abottom surface, and a wall extending therebetween wherein the wall formsan outer surface of the sleeve, the first substance contacting the wallalong a portion thereof and extending partially from the bottom surfaceto the top surface; allowing the first substance to bond to the sleeveand cure to form a composite; disengaging the first mold surface fromthe composite.
 10. A method of forming a composite implant comprising:pouring a first substance between a harvested natural occurring bonesleeve and a first mold surface, the sleeve comprising a top surface, abottom surface, and a wall extending therebetween wherein the wall formsan inner surface of the sleeve, the first substance contacting the wallalong a portion thereof and extending completely from the bottom surfaceto the top surface allowing the first substance to bond to the sleeveand cure to form a composite; disengaging the first mold surface fromthe composite.
 11. A method of forming a composite implant comprising:pouring a first substance between a harvested natural occurring bonesleeve and a first mold surface, the sleeve comprising a top surface, abottom surface, and a wall extending therebetween wherein the wall formsan outer surface of the sleeve, the first substance contacting the wallalong a portion thereof and extending completely from the bottom surfaceto the top surface allowing the first substance to bond to the sleeveand cure to form a composite; disengaging the first mold surface fromthe composite.
 12. A method for forming a composite implant comprising:disposing a moldable substance between a harvested natural occurringannular bone section and a plurality of mold surfaces, the bone sectioncomprising a top surface, a bottom surface, and a wall extendingtherebetween defining an inner surface and an outer surface, themoldable substance contacting the wall along at least a portion thereofso that the substance extends at least partially between the bottomsurface and the top surface; allowing the moldable substance to bond tothe annular bone section to form a composite; disengaging the moldsurfaces from the composite.
 13. The method of claim 12, wherein themoldable substance comprises a viscous polymer.
 14. The method of claim13, wherein the moldable substance further comprises a ceramic fillermaterial.
 15. The method of claim 12, wherein the moldable substancecontacts the outer surface.
 16. The method of claim 12, wherein themoldable substance contacts the inner surface.
 17. The method of claim12, wherein the moldable substance contacts both the outer surface andthe inner surface.
 18. The method of claim 12, wherein the moldablesubstance extends completely from the bottom surface and the topsurface.
 19. The method of claim 12, wherein the bone section ispartially demineralized or demineralized.
 20. The method of claim 12,wherein the bone section comprises allograft bone.